Thanks, Andres. The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. If it is not clear that any of the above strategies are working, it is useful to take a more general approach to verifying the general validity of the model. Stationary (time-invariant) models with nonlinearities may converge very slowly. At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. Segregated approach and Direct vs. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Create the time-dependent step or study. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Perhaps this approach could be adapted to represent your model. The algorithm is, generally speaking, a Newton's method approach. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Consult your product manuals for complete trademark details. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. This is a review for cards & stationery in Brea, CA: "Love this store!!! Screenshot showing a Solver Configuration that has been altered. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The advantages of the continuation method are two-fold. Sometimes, reducing the model complexity can be quite challenging and it can be better to start from as simple a case as possible and gradually increase the complexity. Within either of these features, it can also be helpful to enable the Results While Solving option, as shown in the screenshot below, to visualize the iterations being taken during the solution. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. One can say that, in general, if the loads on a nonlinear system are zero, the system will be at rest; that is, the solution will be zero. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. thanks for reply You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version First, it is physically intuitive, often matching how one would perform an experiment. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. For example, if there is a temperature-dependent material property such as: comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This involves a systematic reduction in the model complexity. Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Discussion Closed This discussion was created more than 6 months ago and has been closed. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Asking for help, clarification, or responding to other answers. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Direct PARDISO Solver , PARDISO . The other low-level default settings within the Stationary Solver are chosen for robustness. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. . Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Use this parameter to modify the nonlinearity expressions in the model. For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Reply . See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. COMSOL does not assume any legal liability for the accuracy of the data disclosed. To switch between these solver types, go to the Stationary Solver node within the Study sequence. You can unsubscribe from these emails at any time. New Stationary Engineer jobs added daily. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. Save my name, email, and website in this browser for the next time I comment. Alternatively, delete and re-create the study. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. Extending this logic, if one wants to solve for any arbitrary load on a nonlinear system, it makes sense to solve a sequence of intermediate problems with gradually increasing load values and using the solutions from each previous step as the initial condition for the next step. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. "After the incident", I started to be more careful not to trip over things. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 It is also possible to manually refine the mesh. Common Mistakes: Not assigning materials to all the domains. The coupling terms between the different groups are thus neglected. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 3. Cooling and Solidification of Metal. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. To switch between these solver types, go to the Stationary Solver node within the Study sequence. This case is generally difficult, or impossible, to solve since this material property is non-smooth. listed if standards is not an option). Posted Sep 9, 2020, 1:44 p.m. EDT Multiphysics problems are often nonlinear. In that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. The default Initial Values for the unknowns in most physics interfaces are zero. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This involves a systematic reduction in the model complexity. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. With respect to multiphysics couplings, rather than solving the problem using a fully coupled approach (the default) solve the problem sequentially, with one physics being solved after another. - Function: ^ Failed to evaluate variable. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. What sort of strategies would a medieval military use against a fantasy giant? The software then computes an initial solution and from there it iteratively re-computes the solution, taking into account how these intermediate solutions affect the nonlinearities. The fully coupled and segregated approaches are discussed below. The settings controlling the predictor type. It is sometimes necessary to manually scale the dependent variables. The segregated approach, on the other hand, solves sets of unknowns separately. - Why? The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. It may also reveal that the model itself is ill-posed in some way. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. COMSOL makes every reasonable effort to verify the information you view on this page. If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions. Connect and share knowledge within a single location that is structured and easy to search. Multiphysics problems are often nonlinear. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. thanks for reply Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Segregated approach and Direct vs. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Please dont hesitate to post comments below or send emails to us if you experience any other problems. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Trying to understand how to get this basic Fourier Series.